Strong methanol masers in the E \(2_0 \rightarrow 3_{-1}\)  transition at 12.178 GHz were discovered in a number of galactic sources including W3(OH) [1]}. Based on the observational data on methanol masers available at that time, [1]} suggested that methanol masers can be divided into two categories. Sources that show maser emission in the \(J_2 \rightarrow J_1\)  series of E-type methanol belong to the first category or class of masers. These masers can be found apart from OH and H\(_2\) O masers, compact H II regions and infrared sources. Second category of masers are found close to compact H II regions. The known at that time methanol transitions at 12.178, 19.967 and 23.121 GHz belong to this category of masers. Surveys of 36.169 and 44.069 GHz methanol transitions towards galactic star-forming regions [3]}, [4]}, [5]}, and interferometric observations of methanol transitions E \(5_{-1} \rightarrow 4_0\)  at 84.521 GHz and A\(^+\)  \(8_0 \rightarrow 7_1\)  at 95.169 GHz [6]}, [7]} revealed that all these lines belong to the first category of masers. The two categories of methanol masers were subsequently labelled as Class I and Class II [8]}.
